1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or a printer, having the function of forming an image on a recording medium, such as a sheet, and more particularly, to a developing apparatus to be provided in such an image forming apparatus.
2. Description of the Related Art
As a conventional development system using a mono-component developer (toner), there has been proposed a contact development system using a developing roller equipped with an elastic layer. In connection with the contact development system, there have been proposed several toner regulating members for forming a thin layer of mono-component toner on a developer carrying member. One of these toner regulating members is described with reference to FIG. 11.
FIG. 11 is a diagram illustrating a contact development system using a developing roller having an elastic layer.
The construction as described below is well known as a contact development system. A developing roller 103 is an elastic roller having a dielectric layer. A nonmagnetic developer is carried on the developing roller 103, which is held in contact with the surface of a photosensitive drum 101 through the intermediation of the nonmagnetic developer. The supply of developer to the developing roller 103 is effected by a supply roller 105 held in contact with the developing roller 103. The supply roller 105 has the function of conveying developer from within a developing container T to the developing roller 103 and of temporarily removing the developer remaining on the developing roller 103.
The layer regulation of the developer adhering to the developing roller 103 and the imparting of electric charge through triboelectrification are effected by causing a toner regulating member 104 to abut the developing roller 103. As an example of the toner regulating member 104, there has been proposed a member of a blade-like configuration formed by a metal thin plate supported in a cantilever-like fashion, with the surface of the metal thin plate abutting the developing roller 103. The developing roller 103 is coated with developer by the toner regulating member. The developer used for the coating serves to develop an electrostatic latent image, formed on the photosensitive drum 101, into a toner image through the electrical potential of a bias applied to the developing roller 103.
Further, in recent years, in order to achieve higher image quality, there has been proposed a reduction in the particle diameter of the toner (see, for example, U.S. Pat. No. 7,313,350).
However, the conventional technique described above has the following problem.
In a developing apparatus adopting the contact development system and using toner of small particle diameter, it is rather difficult to form a coating layer on the developing roller in a stable manner when there is a change in the environment or an increase in the number of sheets on which printing is to be performed. In order to supply toner to the developing roller in a stable manner, it is necessary to increase the surface roughness of the developing roller and to increase the regulating force of the regulating member. This, however, leads to promotion of degeneration of the toner, a marked reduction in durability, and image failure.
Thus, it is difficult to attain both higher image quality and higher durability.